Loud speaker



June 2, 1931.

B. DEMPSTER ET AL LOUD SfEAKER Filed May 6, 1930 IN V EN TOR. BurgeSs Dempscer 'Q BY hr C. can;

40 itself.

Patented June 2, 1931 UNITED STATES PATENT OFF-ICE BURGESS DEMPSTER OF BERKELEY, CALIFORNIA, AND JOHN C. KOONZ, OF EVAN STON, ILLINOIS, ASSIGNORS TO THE MAGNAVOX COMPANY, OF OAKLAND, CALIFORNIA, A

CORPORATION OF ARIZONA LOUD SPEAKER Application filed May 6,

is enclosed and protected by the magnetic field structure. I

The adoption of conical diaphragms to loud speakers of the moving coil type has now become almost universal. These diaphragms are made in various sizes. The most generally accepted sizes range from six inches in diameter upward. With such a large diaphragm it will'be apparent that considerable space will be required for the speaker when it is housed in a cabinet such as a radio console cabinet or the like. All loud speakers of this type up to the present time, so far as we are aware, are constructed with a magnetic field producing element which projects rearwardly and externally of the diaphragm. This construction,-in addition to having the large diameter of the diaphragm as one limitation to its use in confined spaces, also has the additional disadvantage of the large dimension in length. It is therefore another object of our invention to provide a loud speaker in which the magnetic field producing structure may be combined with a diaphragm of the conical type which will not require any considerable additional amount of space over that required by the diaphragm Other objects and advantages to our invention will be in part pointed out and in part evident from the following description taken in connection with the accompanying drawings.

For a better understanding of our invention reference should be had to the accompanying drawings, wherein like numerals refer to like parts throughout the several views.

1930. Serial N0. 450,128.

In the drawings-- Fig. -1 is the front view in elevation of a complete speaker, Fig. 2 is a vertical sectional view taken through the center of the speaker illustrated in Fig. 1,

Fig. 3 is an enlarged sectional view showing a detail of construction where the parts of the magnetic frame structure meet, and

Fig. 4 isan enlarged fragmentary view in section showing a modified form of pole spacing and centering device.

In the drawings 10 designates a relatively fiat plate-like member of magnetic material having four sectors cut out so as to form inwardly projecting portions or spoke members 11, which merge to form a central support for an inner pole piece 12. The pole piece 12 is shown as projecting inwardly from its supporting members 11. A second frame member of magnetic material designated by the numeral 13 is shown as secured to the plate-like member 10 at its outer edge. This second frame member 13 is illustrated as substantially conical in shape and as having a flattened portion 14 at its apex which projects inwardly toward the projecting or inner end of the central pole piece 12. Mounted upon the flattened portion 14 of the frame member 13 we provide an annular pole piece 15 which in conjunction with the pole piece 12 forms an annular air-gap in which a diaphragm actuating coil 16 may operate. The coil 16 is shown as secured to the apex of a conical diaphragm 17 which is secured at its outer rim by means of a flexible skiver 18 to the frame members 10 and 13 at the point where the latter members are secured to gether. At this point and arranged on opposite sides of the skiver 18 there is shown suitable yielding washers 19 of felt or cardboard. These yielding washers 19 are adapted to engage the skiver 18 and permit a relative movement betweenthe frame members 10 and 13 as they are drawn tightly together by the screws 20 to form a tight magnetic fit. At the apex of the diaphragm 17 there is provided a flexible centering means 21 which serves to hold the diaphragm operating coil 16 centrally in the air-gap formed between the same direction.

the inner and outer pole pieces. The centering means 21 as shown is mounted upon one side of the annular pole piece 15.

Secured upon the outer or opposite side of the pole piece 15 we provide a pole centering device 22, which in the embodiment of our invention illustrated in Fig. 2 engages a projection 23 formed upon the end .of the inner pole piece 12. This polo centering device 22 is constructed of a non-magnetic material such as brass or the like and serves to maintain the air-gap between pole pieces 12 and 15 uniform and constant.

In order to energize the magnetic structure described above and to provide a suitable flux in the air-gap in which the cone actuating coil 16 operates, we provide an energizing coil 24. This energizing coil 24 is shown as mounted upon the inner pole piece 12 and disposed within the conical diaphragm 17. The coil 24 will be of such shape and so mounted that it will not interfere with the free movement of the coil 17, and will preferably be firmly held upon the inner pole piece in a positive manner by some suitable means. In the drawings we have illustrated a shoulder 25 upon the pole piece 12 which will serve this function. The provision of the shoulder 25, however, illustrates only one manner of securing the coil 24 in place and it is, therefore, to be understood that the shoulder 25 can be dispensed with where other means of securing the coil 24 in place are provided.

The inner pole supports or portions 11 of the annular member 10 are also shown as reduced in width so as to not materially interfere with the propagation of sound waves by the diaphragm 17 when it is actuated. In order that these portions 11 will have suflicient metallic cross-sectional area to carry the necessary flux, we rivet or otherwise secure thereto additional members 26 of magnetic material which, as will be readily seen, increase the magnetic cross-section of the parts at these points.

By referringto Fig. 3 it will be seen that the annular magnetic frame 10 is provided with a rearwardly projecting flange 27, and that the magnetic frame 13 is also provided with a similar flange 28 which extends in The flanges 27 and 28 upon the members 10 and 13, respectively, are preferably formed at slightly different angles upon their respective members so that when the two are drawn together as by a tightening of the screws 20, the two flanges will be drawn into close magnetic contact. Preferably the flange 28 is flared outwardly, slightly so that as it is drawn into the flange 27 a tight fit will result.

In Fig. 4 we have illustrated a modified form of centering means .for the pole piece of our improved speaker. In this embodiment we show a centering means 29 of non-magnetic material which is so shaped that the projecting end 23, previously described, as provided upon the end of the inner pole piece 12 can be dispensed with. This modified centering means 29, instead of having an opening in the center for a projection upon the pole piece 12, is provided with a depressed portion 30 which is adapted to engage the inner end of the pole piece 12 at a point substantially in line with the face of the outer pole piece 15. Surrounding the depressed portion 30 the centering means 29 may be said to be bowed outwardly from the air gap so as to bridge the latter and provide a suitable space in which the cone actuating coil 16 may freely move. A screw 31 is shown as passing through the centering means 29 and threaded into the end of pole piece 12.

While we have, for the sake of clearness and in order to disclose our invention so that the same can be readily understood, described and illustrated specific devices and arrangements, we desire to have it understood -that this invention is not limited to the specific means disclosed but may be embodied in other ways that will suggest themselves, in view of this broad disclosure, to persons skilled in the art. It is believed that this invention is broadly new and it is desired to claim it as such so that all such changes as come within the scope of the appended claims are to be considered as part of this invention.

Having thus described our invention, what we claim and desire to secure by Letters Patent is 1. In a loud speaker of the moving coil type the combination of, a pair of cooperating frame members of magnetic material, a conical diaphragm supported by said frame mem:

bers, a central pole upon one of said framemembers projecting into said diaphragm and through an opening at its apex, a second pole upon the other of said frame members disposed about the end of said centralpole piece, a current carrying coil secured to said diaphragm at its apex, and an energizing coil upon said central pole disposed within said conical diaphragm, whereby a magnetic field completely surrounding said conical diaphragm will be established.

2. In a loud speaker of the moving coil type the combination of, a pair of cooperating frame members of magnetic material, a conical diaphragm held in clamped engagement between said frame members, a central pole piece upon one of saidframe members projecting axially into said diaphragm and through an opening at its apex, an annular pole piece upon the other of said frame members disposed about the end of said central pole piece, a current carrying coil secured to said diaphragm at its apex, and an energizing coil upon said central pole piece disposed within said conical diaphragm, whereby a tral pole piece forming an air gap in which a said actuating coil is disposed, and a member of non-magnetic material secured to said pole pieces and bridging said air gap for holding said polepieces in spaced relation.

4. In a loud speaker of the moving coil type the combination of, a. central pole iece,

gap, a member of non-magnetic-material on the other side of said annular pole piece adapted to bridgesaid air gap, and means at the end ofsaid central pole adapted to engage said non-magnetic member and hold said central pole piece in concentnc and spaced relation with said annular'pole P1606;

BURGESS DEMPSTER. JOHN C. KOONZ.

a diaphragm actuating coil disposed a out,

the end of said central pole piece, an annular pole piece surrounding the end of said central pole piece forming an air gap in which said actuating coil is disposed, and a member of non-magnetic material secured to said pole pieces for holding them in spaced relation, said member having an annular depression adjacent the air gap in which said diaphragm actuating coil can move.

A magnetic field structure for loud speakers of the moving coil type comprising, a relatively flat annular member of magnetic material having inwardly extending central portions, a central pole piece secured to said central therefrom, a conically shaped frame member of magnetic material cooperatin with said annular member, said latter mem r having an annular pole extremity formed at its apex which surrounds the inner end of said central pole piece, and means carried by said conical shaped frame member engaging the inner end of said central pole piece and adapted to hold said annular pole extremity in spaced relation with the end of said central pole piece.

6. A magnetic field structure for loud speakers of the moving coil type comprising, a relatively flat member of magnetic material having inwardly extending central portions, a central pole piece secured to said central portions and projecting inwardly therefrom, a frame member of magnetic material cooperat ing with said fiat member, said latter member having an annular pole extremity which surropnds the inner end of said central pole piece, and means carried by said frame member engaging the inner end of said central pole piece and adapted to hold said annular pole extremity in spaced relation with the end of said central pole piece.

7. In a loud speaker of the electro-dynamic type the combination of, a central pole piece, a disc like annular pole piece extending at right angles to and surrounding one end of said central pole piece and forming an annular gap in which a diaphragm actuatmg coll may operate, a support upon one side of said annular pole piece for holdin said diaphragm actuating coil centrally in t 0 air portions and projecting inwardly 

